1. Field of the Invention
This invention relates to heterogeneous catalysts and processes using such catalysts for the alkylation of phenols. More particularly, this invention relates to the preparation of ortho-alkylphenols in high purity with a minimum of impurity by-products.
2. Description of the Prior Art
The alkylation of phenols has been carried out using homogeneous aluminum phenoxide catalysts in a pressurized liquid/gas reaction to prepare ortho-alkylphenols. However, such processes commonly produce significant amounts of 2,4-dialkylphenols or 2,4,6-trialkylphenols and suffer from other problems. In particular, current homogeneously catalyzed alkylations have waste problems and require acidification and neutralization steps which increase the overall cost of the process.
U.S. Pat. No. 3,355,504 describes the "ortho catalyst" used for the conversion of an ortho-alkylphenol to a 2,6-dialkylphenol. The ortho catalyst is an aluminum 2-substituted phenoxide which strongly directs the production of 2,6-dialkylphenols rather than the 2,4,6-trialkylphenol. The "ortho catalyst" must be used in the substantial absence of phenol which does not have ortho substituents and ethers such as phenyl butylether which may generate phenol. This is because the phenol tends to replace the ortho-substituted phenol moiety on the aluminum 2-substituted phenoxide catalyst thereby destroying the strong alkylation directing effects.
The process described in U.S. Pat. No. 3,355,504 and other related processes use a homogeneous aluminum phenoxide catalyst which, after alkylation with, e.g., isobutylene, must be acidified for a phase cut followed by neutralization with sodium carbonate so as to avoid corrosion of distillation columns and also avoid dealkylation of product in the columns which are operated at temperatures that might otherwise favor dealkylation. Thereafter, the aqueous phase of the mixture is sent to a caustic solution for precipitation of an aluminum salt which is contaminated with phenol. This presents an immense disposal problem since the aluminum cannot otherwise be used or recovered. In the past, this aluminum precipitate has been disposed of as a phenol-bearing waste stream.
U.S. Pat. No. 3,652,685 describes the separation of aluminum catalyst materials which generate phenol-bearing aluminum waste.